You are taking 'ancestor' in a strict technical sense, which was clearly not my intention.
> though both English and Sanskrit do share a common ancestry several thousand years ago
And those roots can be found and recognized in the subsequent languages, and there lies the value.
Blutly, this was not obvious, and what you suggested would have been equally true if you'd said:
Learn Lithuanian. You were writing in a descendant language just now. If you learnt the roots, you would understand the descendants better.
You did not express that clearly enough then.
It's just that I cannot allocate the safest amount of effort in composing. I thought it was clear enough.
These languages are indeed relatives, literally part of the same family, but we usually distinguish whether they are lineal ancestors or not. If you said "Julia is your grandmother" when Julia was actually the person's aunt, that person might get very confused about your claim!
People's aunts do often have a cultural effect on them, but we can still be more specific and distinguish them from their grandmothers.
The literal matter (of direct inheritance) was meaningless to me in the composition, because the whole point was not and is not "what took from what": the whole point is the contribution that those languages give in the understanding of the current languages they informed.
Only, simply, non technically, that Sanskrit literature happened, then (non-committal irrelevant sketchy for-purpose-of-representation "then") Greek literature happened and you can find the Sanskrit terms modified (not literally them Sanskrit terms, more crisply the presence of the roots) into the Greek terms, and then (again) Latin literature happened, and you can find the Sanskrit and Greek terms modified into the Latin ones, etc.
Phenomenon: "one [as-if] entered into the other"; reality: "a common Language is revealed in their terminology"; the important part: "we can better define the terminology of current languages that share that property through the consideration of the languages that _substantially_ constitute their roots".